REPOST: The Latest Facebook Chain Letter Meme
Note: This was originally published on my old LiveJournal blog back in 2011. The original text can be found at http://tomd1969.livejournal.com/13770.html. I am reposting it here because this is something that seems to crop up every couple of years.
Recently, two friends posted this to their Facebook status updates:
I was just told and I'm not superstitious, but this year July has 5 Fridays, 5 Saturdays and 5 Sundays. This happens once every 823 years. This is called money bags. So, copy this to your status and money will arrive within 4 days. Based on Chinese Feng Shui. The one who does not copy will be without money. I cannot let that person be.............. ME! Good Luck
This is incorrect. I'm going to ignore the superstitious aspects (and the Feng Shui, which is used here in a way I'm unfamiliar with) for a moment, and focus on what I can prove.
Whoever originally wrote this apparently has no idea how the Gregorian calendar works: The calendars recycle every 400 years. That means that the calendar for 2000 would have been the same as the calendar for the year 1600 (Although the RC Church adopted the Gregorian calendar in 1582, the British Empire, and thus the American colonies, did not adopt it until 1752). In turn, this means that the calendar for 2011 is exactly the same as the calendar for 1611 and will be the same for the calendar for 2411. Therefore, at the very minimum, 823 years is wrong and should be 400 years.
But even that would have been wrong.
A July that has 5 Fridays, Saturdays and Sundays must have started on a Friday (that would make the 29th a Friday, the 30th a Saturday, and the 31st a Sunday, which would be the 5th Friday, Saturday, and Sunday of that month). Since 1900, this has happened 15 times: 1904, 1910, 1921, 1927, 1932, 1938, 1949, 1955, 1960, 1966, 1977, 1983, 1988, 1994, and 2005. This means that on average in the last 111 years, it has happened every 7.133 years.